Method and apparatus for motion vector prediction using spatial and temporal combination

ABSTRACT

A method of video decoding for a video decoder that includes acquiring a current picture from a coded video bitstream. The method further includes selecting, from a history buffer that stores motion vector predictors of N previously decoded blocks. The method further includes selecting, from the history buffer, a second motion vector predictor of a second neighboring block of the current block. The method further includes selecting a first temporal block included in a previously decoded reference picture associated with the current picture, the first temporal block including a third motion vector predictor, the first temporal block being one of (i) neighboring to a collocated block of the current block and (ii) within the collocated block. The method further including determining a motion vector predictor of the current block using a weighted average of the first motion vector predictor, the second motion vector predictor, and the third motion vector predictor.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/711,394, “MOTION VECTOR PREDICTION USINGSPATIAL AND TEMPORAL COMBINATION” filed on Jul. 27, 2018, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding using inter-picture prediction with motioncompensation has been known for decades. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce aforementioned bandwidth or storage space requirements,in some cases by two orders of magnitude or more. Both lossless andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between theoriginal and reconstructed signal is small enough to make thereconstructed signal useful for the intended application. In the case ofvideo, lossy compression is widely employed. The amount of distortiontolerated depends on the application; for example, users of certainconsumer streaming applications may tolerate higher distortion thanusers of television contribution applications. The compression ratioachievable can reflect that: higher allowable/tolerable distortion canyield higher compression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived fromneighboring area's MVs. That results in the MV found for a given area tobe similar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

A history buffer of motion vector predictors may be used to performencoding or decoding. Generally, the maintenance of the history bufferis performed after each block, in encoding or decoding order, iscompleted. If this block is coded in inter mode with a set of MVinformation, the MV of this block is put into a history motion vectorpredictor (HMVP) buffer for updating the buffer. When encoding ordecoding the current block, the MV predictors for the current block maycome from previously coded spatial/neighboring blocks at fixedpositions, which may not lead to the most accurate motion vectorprediction.

SUMMARY

An exemplary embodiment includes a method of video decoding for a videodecoder. The method includes acquiring a current picture from a codedvideo bitstream and selecting, from a history buffer that stores motionvector predictors of N previously decoded blocks from the currentpicture, a first motion vector predictor of a first neighboring block ofa current block in the current picture, N being an integer greaterthan 1. The method further includes selecting, from the history buffer,a second motion vector predictor of a second neighboring block of thecurrent block. The method further includes selecting a first temporalblock included in a previously decoded reference picture associated withthe current picture, the first temporal block including a third motionvector predictor, the first temporal block being one of (i) neighboringto a collocated block of the current block and (ii) within thecollocated block. The method also includes determining a motion vectorpredictor of the current block using a weighted average of the firstmotion vector predictor, the second motion vector predictor, and thethird motion vector predictor.

An exemplary embodiment includes a video decoder for video decoding thatincludes processing circuitry. The processing circuitry is configured toacquire a current picture from a coded video bitstream, and select, froma history buffer that stores motion vector predictors of N previouslydecoded blocks from the current picture, a first motion vector predictorof a first neighboring block of a current block in the current picture,N being an integer greater than 1. The processing circuitry is furtherconfigured to select, from the history buffer, a second motion vectorpredictor of a second neighboring block of the current block. Theprocessing circuitry is further configured to select a first temporalblock included in a previously decoded reference picture associated withthe current picture, the first temporal block including a third motionvector predictor, the first temporal block being one of (i) neighboringto a collocated block of the current block and (ii) within thecollocated block. The processing circuitry is further configured todetermine a motion vector predictor of the current block using aweighted average of the first motion vector predictor, the second motionvector predictor, and the third motion vector predictor.

An exemplary embodiment includes a non-transitory computer readablemedium having instructions stored therein, which when executed by aprocessor in a video decoder causes the video decoder to execute amethod. The method includes acquiring a current picture from a codedvideo bitstream and selecting, from a history buffer that stores motionvector predictors of N previously decoded blocks from the currentpicture, a first motion vector predictor of a first neighboring block ofa current block in the current picture, N being an integer greaterthan 1. The method further includes selecting, from the history buffer,a second motion vector predictor of a second neighboring block of thecurrent block. The method further includes selecting a first temporalblock included in a previously decoded reference picture associated withthe current picture, the first temporal block including a third motionvector predictor, the first temporal block being one of (i) neighboringto a collocated block of the current block and (ii) within thecollocated block. The method also includes determining a motion vectorpredictor of the current block using a weighted average of the firstmotion vector predictor, the second motion vector predictor, and thethird motion vector predictor.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system (100) in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 6 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 7 is a schematic illustration of a current block and surroundingspatial merge candidates.

FIG. 8 is a schematic illustration of merge candidate list construction.

FIG. 9 is schematic illustration of extended merge mode.

FIGS. 10A and 10B illustrate an embodiment of a history based motionvector prediction buffer.

FIG. 11 is a schematic illustration of selection of two spatialcandidates in a spatial-temporal motion vector prediction mode.

FIG. 12 is a schematic illustration of intra picture block compensation.

FIG. 13 is a schematic illustration of example candidate locations fortemporal motion vector prediction.

FIG. 14 illustrates an embodiment of a process performed by an encoderor a decoder.

FIG. 15 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. Thecommunication system (100) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (150). Forexample, the communication system (100) includes a first pair ofterminal devices (110) and (120) interconnected via the network (150).In the FIG. 1 example, the first pair of terminal devices (110) and(120) performs unidirectional transmission of data. For example, theterminal device (110) may code video data (e.g., a stream of videopictures that are captured by the terminal device (110)) fortransmission to the other terminal device (120) via the network (150).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (120) may receive the codedvideo data from the network (150), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (100) includes a secondpair of terminal devices (130) and (140) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (130) and (140)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (130) and (140) via the network (150). Eachterminal device of the terminal devices (130) and (140) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (130) and (140), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 1 example, the terminal devices (110), (120), (130) and(140) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (150) represents any number ofnetworks that convey coded video data among the terminal devices (110),(120), (130) and (140), including for example wireline (wired) and/orwireless communication networks. The communication network (150) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(150) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating forexample a stream of video pictures (202) that are uncompressed. In anexample, the stream of video pictures (202) includes samples that aretaken by the digital camera. The stream of video pictures (202),depicted as a bold line to emphasize a high data volume when compared toencoded video data (204) (or coded video bitstreams), can be processedby an electronic device (220) that includes a video encoder (203)coupled to the video source (201). The video encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (204) (or encoded video bitstream (204)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (202), can be stored on a streamingserver (205) for future use. One or more streaming client subsystems,such as client subsystems (206) and (208) in FIG. 2 can access thestreaming server (205) to retrieve copies (207) and (209) of the encodedvideo data (204). A client subsystem (206) can include a video decoder(210), for example, in an electronic device (230). The video decoder(210) decodes the incoming copy (207) of the encoded video data andcreates an outgoing stream of video pictures (211) that can be renderedon a display (212) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (204),(207), and (209) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Codingor VVC. The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (220) and (230) can includeother components (not shown). For example, the electronic device (220)can include a video decoder (not shown) and the electronic device (230)can include a video encoder (not shown) as well.

FIG. 3 shows a block diagram of a video decoder (310) according to anembodiment of the present disclosure. The video decoder (310) can beincluded in an electronic device (330). The electronic device (330) caninclude a receiver (331) (e.g., receiving circuitry). The video decoder(310) can be used in the place of the video decoder (210) in the FIG. 2example.

The receiver (331) may receive one or more coded video sequences to bedecoded by the video decoder (310); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (301), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (331) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (331) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween the receiver (331) and an entropy decoder/parser (320) (“parser(320)” henceforth). In certain applications, the buffer memory (315) ispart of the video decoder (310). In others, it can be outside of thevideo decoder (310) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (310), forexample to combat network jitter, and in addition another buffer memory(315) inside the video decoder (310), for example to handle playouttiming. When the receiver (331) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (315) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (315) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (310).

The video decoder (310) may include the parser (320) to reconstructsymbols (321) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (310),and potentially information to control a rendering device such as arender device (312) (e.g., a display screen) that is not an integralpart of the electronic device (330) but can be coupled to the electronicdevice (330), as was shown in FIG. 3. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (320) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (320) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer memory (315), so as to createsymbols (321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (310)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). The scaler/inversetransform unit (351) can output blocks comprising sample values, thatcan be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (358). The currentpicture buffer (358) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(355), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (352) has generated to the outputsample information as provided by the scaler/inverse transform unit(351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (351) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (357) from where themotion compensation prediction unit (353) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (353) in the form of symbols (321) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (357) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (356) as symbols (321) from the parser (320), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (312) as well as stored in the referencepicture memory (357) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (320)), the current picture buffer (358) can becomea part of the reference picture memory (357), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (310) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as document in thevideo compression technology or standard. Specifically, a profile canselect a certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (331) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (310) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 4 shows a block diagram of a video encoder (403) according to anembodiment of the present disclosure. The video encoder (403) isincluded in an electronic device (420). The electronic device (420)includes a transmitter (440) (e.g., transmitting circuitry). The videoencoder (403) can be used in the place of the video encoder (203) in theFIG. 2 example.

The video encoder (403) may receive video samples from a video source(401)(that is not part of the electronic device (420) in the FIG. 4example) that may capture video image(s) to be coded by the videoencoder (403). In another example, the video source (401) is a part ofthe electronic device (420).

The video source (401) may provide the source video sequence to be codedby the video encoder (403) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . )and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (401) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (401) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focusses on samples.

According to an embodiment, the video encoder (403) may code andcompress the pictures of the source video sequence into a coded videosequence (443) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (450). In some embodiments, the controller(450) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (450) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (450) can be configured to have other suitablefunctions that pertain to the video encoder (403) optimized for acertain system design.

In some embodiments, the video encoder (403) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (430) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (433)embedded in the video encoder (403). The decoder (433) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (434). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (434) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchroni city (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder, such as the video decoder (310), which has alreadybeen described in detail above in conjunction with FIG. 3. Brieflyreferring also to FIG. 3, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (445) and the parser (320) can be lossless, the entropy decodingparts of the video decoder (310), including the buffer memory (315), andparser (320) may not be fully implemented in the local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (430) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (432) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (433) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (434). In this manner, the video encoder(403) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new picture to be coded, the predictor(435) may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the source coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder (445)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (403) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the video encoder (403).During coding, the controller (450) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of Intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (403) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (403) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The source coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to Intra prediction) makes uses of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first and a second reference picture thatare both prior in decoding order to the current picture in the video(but may be in the past and future, respectively, in display order) areused. A block in the current picture can be coded by a first motionvector that points to a first reference block in the first referencepicture, and a second motion vector that points to a second referenceblock in the second reference picture. The block can be predicted by acombination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one coding unit (CU) of 64×64 pixels, or 4 CUs of 32×32pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed todetermine a prediction type for the CU, such as an inter prediction typeor an intra prediction type. The CU is split into one or more predictionunits (PUs) depending on the temporal and/or spatial predictability.Generally, each PU includes a luma prediction block (PB), and two chromaPBs. In an embodiment, a prediction operation in coding(encoding/decoding) is performed in the unit of a prediction block.Using a luma prediction block as an example of a prediction block, theprediction block includes a matrix of values (e.g., luma values) forpixels, such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels andthe like.

FIG. 5 shows a diagram of a video encoder (503) according to anotherembodiment of the disclosure. The video encoder (503) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (503) is used in theplace of the video encoder (203) in the FIG. 2 example.

In an HEVC example, the video encoder (503) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (503) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (503) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(503) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (503) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 5 example, the video encoder (503) includes the interencoder (530), an intra encoder (522), a residue calculator (523), aswitch (526), a residue encoder (524), a general controller (521) and anentropy encoder (525) coupled together as shown in FIG. 5.

The inter encoder (530) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique.

The intra encoder (522) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform and, in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques).

The general controller (521) is configured to determine general controldata and control other components of the video encoder (503) based onthe general control data. In an example, the general controller (521)determines the mode of the block, and provides a control signal to theswitch (526) based on the mode. For example, when the mode is the intra,the general controller (521) controls the switch (526) to select theintra mode result for use by the residue calculator (523), and controlsthe entropy encoder (525) to select the intra prediction information andinclude the intra prediction information in the bitstream; and when themode is the inter mode, the general controller (521) controls the switch(526) to select the inter prediction result for use by the residuecalculator (523), and controls the entropy encoder (525) to select theinter prediction information and include the inter predictioninformation in the bitstream.

The residue calculator (523) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (522) or the inter encoder (530). Theresidue encoder (524) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (524) is configured to convert the residuedata in the frequency domain, and generate the transform coefficients.The transform coefficients are then subject to quantization processingto obtain quantized transform coefficients.

The entropy encoder (525) is configured to format the bitstream toinclude the encoded block. The entropy encoder (525) is configured toinclude various information according to a suitable standard, such asHEVC standard. In an example, the entropy encoder (525) is configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. Note that, according to the disclosed subject matter, whencoding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 6 shows a diagram of a video decoder (610) according to anotherembodiment of the disclosure. The video decoder (610) is configured toreceive a coded pictures that are part of a coded video sequence, anddecode the coded picture to generate a reconstructed picture. In anexample, the video decoder (610) is used in the place of the videodecoder (210) in the FIG. 2 example.

In the FIG. 6 example, the video decoder (610) includes an entropydecoder (671), an inter decoder (680), a residue decoder (673), areconstruction module (674), and an intra decoder (672) coupled togetheras shown in FIG. 6.

The entropy decoder (671) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example,intra, inter, b-predicted, the latter two in merge submode or anothersubmode), prediction information (such as, for example, intra predictioninformation or inter prediction information) that can identify certainsample or metadata that is used for prediction by the intra decoder(672) or the inter decoder (680) respectively residual information inthe form of, for example, quantized transform coefficients, and thelike. In an example, when the prediction mode is inter or bi-predictedmode, the inter prediction information is provided to the inter decoder(680); and when the prediction type is the intra prediction type, theintra prediction information is provided to the intra decoder (672). Theresidual information can be subject to inverse quantization and isprovided to the residue decoder (673).

The inter decoder (680) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (672) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (673) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (673) mayalso require certain control information (to include the QuantizerParameter QP), and that information may be provided by the entropydecoder (671) (datapath not depicted as this may be low volume controlinformation only).

The reconstruction module (674) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (673) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (203), (403) and (503), and thevideo decoders (210), (310) and (610) can be implemented using anysuitable technique. In an embodiment, the video encoders (203), (403)and (503), and the video decoders (210), (310) and (610) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (203), (403) and (403), and the videodecoders (210), (310) and (610) can be implemented using one or moreprocessors that execute software instructions.

Merge candidates may be formed by checking motion information fromeither spatial or temporal neighbouring blocks of the current block.Referring to FIG. 7, a current block (701) comprises samples that havebeen found by the encoder/decoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. In some embodiments, instead of coding that motionvector directly, the motion vector can be derived from metadataassociated with one or more reference pictures, for example, from a mostrecent (in decoding order) reference picture, using the motion vectorassociated with either one of five surrounding samples, denoted D, A, C,B, and E (702 through 706, respectively). The blocks A, B, C, D, and Emay be referred to as spatial merge candidates. These candidates may besequentially checked into a merge candidate list. A pruning operationmay be performed to make sure duplicated candidates are removed from thelist. An index may be signaled, which identifies the candidates to beused.

In some embodiments, after putting spatial candidates into the mergelist, temporal candidates are also checked into the list. For example, acurrent block's collocated block in a specified reference picture isfound. The motion information at the CO position (707) in the referencepicture is used as a temporal merge candidate. The CO position may be ablock in the reference picture in which the top left corner of thisblock is at a bottom right corner of a collocated block in the referencepicture of the current block 701. The collocated block in the referencepicture may include the same position coordinates (e.g., x and ycoordinates) as the current block 701. If the block at the CO position(707) is not coded in an inter mode or is not available, the block atthe C1 position may be used. The block at the C1 position may have a topleft corner at a center location (e.g., w/2, h/2) of a block within thecollocated block in the reference picture. Particularly, the block atposition C1 may be a sub-block of the collocated block in the referencepicture. In the above example, w and h are the width and height of theblock, respectively. According to some embodiments, additional mergecandidates include combined bi-predictive candidates and zero motionvector candidates.

A skip mode may be used to indicate for a block that the motion data isinferred instead of explicitly signaled and that the prediction residualis zero (i.e., no transform coefficients are transmitted). At thebeginning of each CU in an inter-picture prediction slice, a skip flag(e.g., skip flag) may be signaled that implies one or more of thefollowing: (i) the CU only contains one PU (e.g., 2N×2N); (ii) the mergemode is used to derive the motion data; or (iii) no residual data ispresent in the bitstream.

According to some embodiments, sub-CU modes are enabled as additionalmerge candidates. In some embodiments, no additional syntax element isused to signal the sub-CU modes. In some embodiments, two additionalmerge candidates are added to the merge candidates list of each CU torepresent an alternative temporal motion vector prediction (ATMVP) modeand a spatial-temporal motion vector prediction (STMVP) mode.

A sequence parameter set may indicate the number of candidates in themerge list. For example, up to seven merge candidates may be used in themerge list if a sequence parameter set indicates that ATMVP and STMVPare enabled. The encoding logic of the additional merge candidates maybe the same as for the other merge candidates in the merge candidatelist, which results in, for each CU in P or B slice, two morerate-distortion (RD) checks being performed for the two additional mergecandidates. The order of the merge candidates may be A, B, C, D, ATMVP,STMVP, E (when the merge candidates in the list are less than 6),temporal candidates, combined bi-predictive candidates, and zero motionvector candidates. The merge candidate list may be referenced by a mergeindex. In some embodiments, all bins of the merge index are contextcoded by context-adaptive binary arithmetic coding (CABAC). In otherembodiments, only the first bin is context coded and the remaining binsare context by-pass coded.

According to some embodiments, candidate motion vectors are searchedfrom previously coded blocks, with a step size of 8×8 blocks. FIG. 8illustrates a current block 800 surrounded by 8×8 blocks. The nearestspatial neighbors are category 1 candidates, and include the immediatetop row (i.e., row including blocks mv0 and mv1), left column (i.e.,column including mv2), and top-right corner (i.e., mv2) as category 1.The category 2 candidates may include outer region blocks away from acurrent block boundary and that are collocated in a previously codedframe. The category 2 candidates may include a maximum of threecandidates. In FIG. 8, the category 2 candidates may be selected fromthe outer top row (i.e., row including blocks mv4 and mv5) and the outerleft column (i.e., column including blocks mv5 and mv6). The neighboringblocks that are predicted from different reference frames or are intracoded may be pruned from the list. The remaining reference blocks may beeach assigned a weight. The weight may be related to a distance to thecurrent block. As an example, referring to FIG. 8, the candidate listmay include the following category 1 candidates: mv1, mv0, mv2, and mv3.The candidate list may further include the following category 2candidates: mv5, mv6, and mv4.

According to some embodiments, an extended merge mode includesadditional merge candidates that include blocks that are not immediatelynext to the current block. These candidates may be in the left, top,left bottom, top right, and top left directions. The maximum number ofmerge candidates may be 10. FIG. 9 illustrates a current block 900surrounded to the left, top left, top, and top right by reference blocks(i.e., blocks having diagonal line pattern). The reference blocks mayinclude neighboring blocks A, B, C, D, and E, which correspond to blocksA, B, C, D, and E, respectively, in FIG. 7. In FIG. 9, the top leftcorner of a reference block may have an offset of (−96, −96) withrespect to the current block 900. Each candidate block B (i, j) or C (i,j) may have an offset of 16 in the vertical direction compared to itsprevious B or C candidate blocks, respectively. Each candidate block A(i, j) or D (i, j) may have an offset of 16 in the horizontal directioncompared to its previous A or D candidate blocks, respectively. Each E(i, j) block may have an offset of 16 in both the horizontal andvertical directions compared to its previous E candidates. Thecandidates may be checked in a direction from the reference blocksclosest to current block 900 to the reference blocks farthest from thecurrent block 900. The order of candidates checked may be A (i, j), B(i, j), C (i, j), D (i, j), and E (i, j).

In FIG. 9, the extended neighboring positions may be determined relativeto the current block 900 or relative to a current picture including thecurrent block 900. According to some embodiments, instead of fetchingvalues from these extended neighboring positions, N previously codedblocks' motion information are stored in a HMVP buffer to provide moremotion vector prediction candidates. The HMVP buffer may includemultiple HMVP candidates, and may be maintained during theencoding/decoding process. In some embodiments, the HMVP buffer mayoperate in a first-in-first-out (FIFO) principle such that the mostrecent coded motion information may be considered first when this HMVPbuffer is used during a motion vector prediction process such as themerge mode or the AMVP mode.

FIGS. 10A and 10B illustrate an HMVP buffer before and after a candidateis inserted, respectively. As illustrated in FIGS. 10A and 10B, the HMVPbuffer includes 5 entries with the index [0] to [4]. In FIG. 10B, theentry CL_0 is inserted at index [4], which causes the other entries tomove to the left by one, resulting in the entry HMPV_0 being removedfrom the buffer. The entry CL_0 may include motion vector predictorinformation of a previously encoded or decoded block.

According to some embodiments, motion vector prediction is performed byusing a weighted average of multiple motion vector predictors, where twospatial neighboring blocks' motion vectors and one temporal motionvector are combined to generate a final predictor. For example, asillustrated in FIG. 11 when performing motion vector prediction forcurrent block 1100, a faraway top (Afar) neighbor and left (Lfar)neighbor are checked first. If these neighbors are not available, animmediate top (Amid) neighbor and a left (Lmid) middle neighbor arechecked to substitute the faraway neighbor on the same side. Thetemporal neighbor motion vectors may be obtained from temporal blocks C0(707) and C1 (708), as illustrated in FIG. 7. In FIG. 11, the Afarneighbor has coordinates (nPbW*5/2, −1), the Amid neighbor hascoordinates (nPbW/2, −1), the Lmid neighbor has coordinates (−1,nPbH/2), and the Lfar neighbor has coordinates (−1, nPbH*5/2), wherenPbH is the height of current block 1100 and nPbW is the width ofcurrent block 1100.

In some embodiments, the combination of the vectors obtained for currentblock 1100 is performed as follows:

mvLX[0]=((mvLX A[0]+mvLX L[0]+mvLX C[0])*43)/128,   Eq. 1:

mvLX[1]=((mvLX A[1]+mvLX L[1]+mvLX C[1])*43)/128,   Eq. 2:

where mvLX[n] is the x and y components of the final motion vectorpredictor; mvLX_A[n] is the x and y components of the above predictor;mvLX_L[n] is the x and y components of the left predictor; and mvLX_C[n]is the x and y components of the collocated temporal predictor (n=0, 1).If only two vectors are available, then the average of these two vectorsmay be used as the final motion vector predictor.

Block based compensation from a different picture may be referred to asmotion compensation. Block compensation may also be done from apreviously reconstructed area within the same picture, which may bereferred to as intra picture block compensation or intra block copy. Forexample, a displacement vector that indicates an offset between acurrent block and the reference block is referred to as a block vector.According to some embodiments, a block vector points to a referenceblock that is already reconstructed and available for reference. Also,for parallel processing consideration, a reference area that is beyond atile/slice boundary or wavefront ladder-shaped boundary may also beexcluded from being referenced by the block vector. Due to theseconstraints, a block vector may be different from a motion vector inmotion compensation, where the motion vector can be at any value(positive or negative, at either x or y direction).

FIG. 12 illustrates an embodiment of intra picture block compensation(e.g., intra block copy mode). In FIG. 12, a current picture 1200includes a set of blocks that have already been coded/decoded (i.e.,gray colored blocks) and a set of blocks that have yet to becoded/decoded (i.e., white colored blocks). A sub-block 1202 of one ofthe blocks that have yet to be coded/decoded may be associated with ablock vector 1204 that points to another sub-block 1206 that haspreviously been coded/decoded. Accordingly, any motion informationassociated with the sub-block 1206 may be used for the coding/decodingof sub-block 1202.

The embodiments of the present disclosure provide several methods ofimproving motion vector predictors for inter-picture prediction coding.Some embodiments are directed to methods for generating a motion vectorpredictor from a combination of the HMVP buffer (FIGS. 10A and 10B) andthe TMVP. The embodiments of the present disclosure may be applied toboth merge mode or motion vector prediction with difference coding (AMVPmode). The embodiments of the present disclosure may be easily extendedto any video coding method that uses the merge and general motion vectorprediction concepts. Furthermore, since the skip mode uses the mergemode to derive the motion information, the embodiments of the presentdisclosure may also be applied to the skip mode.

According to some embodiments, a final motion vector predictor isdetermined from two spatial motion vector predictors and a temporalmotion vector predictor. In block based STMVP derivation, two spatialcandidates are derived from top (or top-right) corner (e.g., candidatesE, B, and C in FIG. 7) and left (or bottom-left) corner (e.g.,candidates A and D) of the current block. In some embodiments, the twospatial candidates are derived from two entries of the HMVP buffer,which contains N recently encoded/decoded motion vectors. N may be aninteger number greater than or equal to 2. The final predictor may bethe weighted average of the temporal predictor and three predictors.

In some embodiments, the two spatial motion vector predictors areselected as the last two coded motion vectors in the HMVP buffer (e.g.,HMVP_3 and HMVP_4 in FIG. 10A). In another embodiment, the motion vectorof the last coded block from left neighbors in the HMVP buffer and themotion vector of the last coded block from above neighbors in the HMVPbuffer are used as STMVP spatial candidates. An above neighbor to thecurrent block may be defined as a neighbor block that has its ycoordinate smaller than the current block. Similarly, a left neighbormay be defined as a neighbor block that has its x coordinate smallerthan the x coordinate of the current block.

A neighbor may be both above and left to the current block. The locationof each coded block may be recorded when its motion vector is put in theHMVP buffer, or the location can be derived based on location info(e.g., x, y coordinates of a block) recorded in the HMVP. In someembodiments, a neighbor that is above a current block, but not left atthe same time, and a neighbor that is left of the current block, but notabove at the same time, may be preferred over other candidates in thecandidate selection. If no above or left neighbor is found from the HMVPbuffer, the last coded, but not duplicated motion vector, may be used asone of the STMVP spatial candidates for determining the final motionvector predictor.

In another embodiment, the motion vector of the coded block from theleft neighbors in the HMVP buffer with the longest distance to thecurrent block, and the motion vector of the last coded block from theabove neighbors in the HMVP buffer with longest distance to the currentblock are used as the STMVP spatial candidates for determining the finalmotion vector predictor. The location of each coded block may berecorded when its motion vector is put in the HMVP buffer so that itsdistance to the current block may be calculated. In another example, thelocation of each coded block may be derived, as discussed above.

In another embodiment, the two motion vectors with a highest occurrencein the HMVP buffer are selected as the STMVP spatial candidates fordetermining the final motion vector predictor. When two entries in theHMVP buffer have the same number of occurrence, the entry coded later indecoder order may be selected first.

According to some embodiments, a final motion vector predictor isdetermined using three motion vector predictors from three correspondingSTMVP spatial candidates and one motion vector predictor from acorresponding temporal candidate. Two of the STMVP spatial candidatesmay be derived from top (or top-right) and left (or bottom-left) cornersof the current block. Furthermore, one temporal MV predictor is obtainedfrom one of temporal blocks C0 (707) and C1 (708), as illustrated inFIG. 7.

In some embodiments the three spatial candidates are derived from threeentries of the HMVP buffer, which contains N recently encoded/decodedmotion vectors, where N is an integer number greater than or equal to 3.In one embodiment, the three spatial candidates are selected as the lastthree coded MVs in the HMVP buffer. The final predictor may be aweighted average of the four predictors, as described in further detailbelow. In another embodiment, the three motion vectors with a highestoccurrence in the HMVP buffer are selected as the three spatialcandidates. When two entries in the HMVP buffer have the same number ofoccurrence, the entry coded later in decoder order may be selectedfirst.

According to some embodiments, a final motion vector predictor isdetermined using two motion vector predictors from two correspondingSTMVP spatial candidates and two temporal motion vector predictors fromtwo temporal candidates. The two STMVP spatial candidates may be derivedfrom top (or top-right) and left (or bottom-left) corners of the currentblock. Two of the STMVP spatial candidates may be derived from top (ortop-right) and left (or bottom-left) corners of the current block.

In some embodiments the two spatial candidates are derived from threeentries of the HMVP buffer, which contains N recently encoded/decodedmotion vectors, where N is an integer number greater than or equal to 2.In one embodiment, the two spatial candidates are selected as the lasttwo coded motion vectors in the HMVP buffer. In some embodiments, themotion vector of the last coded block from the left neighbors of thecurrent block in the HMVP buffer, and the motion vector of the lastcoded block from above neighbors of the current block in the HMVP bufferare used as the STMVP spatial candidates. The above and left neighborsmay be defined as discussed above. The location of each coded block maybe recorded when its motion vector is put in the HMVP buffer, or themotion vector may be derived as discussed above. In some embodiments, aneighbor that is above a current block, but not left at the same time,and a neighbor that is left of the current block, but not above at thesame time, may be preferred in the candidate selection. If no above orleft neighbor is found from the HMVP buffer, the last coded, but notduplicated motion vector, may be used as one of the STMVP spatialcandidates for determining the final motion vector predictor.

In another embodiment, the motion vector of the coded block from theleft neighbors in the HMVP buffer with the longest distance to thecurrent block, and the motion vector of the last coded block from aboveneighbors in the HMVP buffer with longest distance to the current blockare used as the STMVP spatial candidates for determining the finalmotion vector predictor. As discussed above, the location of each codedblock may be recorded when its motion vector is put in the HMVP bufferso that its distance to the current block may be calculated, or thelocation of each coded block may be derived.

In another embodiment, the two motion vectors with a highest occurrencein the HMVP buffer are selected as the STMVP spatial candidates fordetermining the final motion vector predictor. When two entries in theHMVP buffer have the same number of occurrence, the entry coded later indecoder order may be selected first.

In some embodiments, the two temporal candidates may be from differentcollocated positions of the current block. FIG. 13 illustrates examplecandidates C0-C8 of a block 1300 that is collocated to a current block.The candidates C0 and C1 correspond to the candidates C0 and C1 in FIG.7, respectively. In some embodiments, the two temporal candidates may befrom the C0 and C1 positions. In another embodiment, the two temporalcandidates may be from the C0 and C2 positions. In another embodiment,the two temporal candidates maybe from any two of the C0-C8 positions,where those positions represent top-left corner (C2), top-middle (C3),top-right corner (C4), middle-left (C5), middle (C1), middle-rightcorners (C6), bottom-left corner (C7), bottom-middle (C8), andbottom-right corner (C8). In some embodiments, the exact location ofeach corner can be any of the smallest blocks near the corner. In thisregard, a location may have four neighboring blocks around the location.For example, in FIG. 13, block C1, the block above C1, the block left toC1, and the block in the above-left position to C1 can all be used torepresent a center location of the whole block 1300.

According to some embodiments, when some of the motion vector candidatesare not available, the actual available number of candidates may be usedfor generating the final predictor, where the calculation should isadjusted to compensate for the unavailable motion vector.

In some embodiments, when all four motion vector candidates areavailable, the final motion vector predictor is determined as:

Final MVP=(MVP1+MVP2+MVP3+MVP4)/4,   Eq. 3:

where MVP1 is the first motion vector predictor, MVP2 is the secondmotion vector predictor, MVP3 is the third motion vector predictor, andMVP4 is the fourth motion vector predictor.

In some embodiments, when two spatial motion vector candidates (MVP1 andMVP2) and one temporal motion vector candidate (MVP3) are available, thefinal motion vector predictor is determined as:

Final MVP=(MVP1+MVP2+MVP3)*43/128, or   Eq. 4:

Final MVP=(MVP1+MVP2+MVP3)/3   Eq. 5:

In some embodiments, when three spatial motion vector candidates (MVP1,MVP2, and MVP3) are available, the final motion vector final motionvector predictor is determined as:

Final MVP=(MVP1+MVP2+MVP3)*43/128 or (MVP1+MVP2+MVP3)/3.   Equ. 6:

In some embodiments, when one spatial motion vector candidate (MVP1) andtwo temporal motion vector candidates (MVP2 and MVP3) are available, thefinal motion vector predictor is determined as:

Final MVP=(MVP1+MVP2+MVP3)43*/128, or   Eq. 7:

Final MVP=(MVP1+MVP2+MVP3)/3.   Eq. 8:

In some embodiments, when two motion vector candidates (MVP1 and MVP2),either spatial or temporal, are available, the final MVP is determinedas:

Final MVP=(MVP1+MVP2)/2.   Eq. 9:

Generally, a collocated picture may be any of the reference pictures ina reference picture list. A reference picture may be chosen from thereference picture list to select a picture as the collocated picture toderive temporal motion vector predictors. In some embodiments, a syntaxflag “slice_temporal_mvp_enabled_flag” is used to indicate if temporalmotion vector prediction is allowed in a current slice or picture, orother level of a process unit. If temporal motion vector prediction isallowed, a syntax flag “collocated_ref_idx” may be used to indicate thereference index of the selected reference picture in the list as thecollocated reference picture. When there is only one reference pictureor no reference picture in the list, the “collocated_ref_idx” flag isnot signaled, and the value of collocated_ref_idx is inferred to be 0 sothat the first reference picture in the list is selected.

According to some embodiments, when the current decoded picture istreated as a reference picture, this reference picture will be placedwith other temporal reference picture(s) in the same list. Inparticular, when a reference picture list is chosen to select acollocated reference picture, if the current decoded picture is the onlyreference picture in the list, the syntax flag for indicating temporalmotion vector prediction (i.e., “slice_temporal_mvp_enabled_flag”) isnot signaled and inferred to be 0. In another example, if the currentdecoded picture is the only reference picture in the list, the syntaxflag for indicating temporal motion vector prediction (i.e.,“slice_temporal_mvp_enabled_flag”) is signaled with a value that is 0.

In some embodiments, if the current decoded picture and another temporalreference picture are the only two reference pictures in the list, thesyntax flag “collocated_ref_idx”, is not signaled and is inferred to be0 if the temporal reference picture is in position 0 of the list, or isinferred as a value that indicates that the temporal reference pictureis the collocated picture. In another example, if the current decodedpicture and another temporal reference picture are the only tworeference pictures in the list, the syntax flag “collocated_ref_idx” issignaled as the value 0 if temporal reference picture is in position 0,or the flag is signaled as a value that indicates that the temporalreference picture is the collocated picture.

FIG. 14 illustrates an embodiment of a process performed by an encodersuch as video encoder 503 or a decoder such as video decoder 610. Theprocess may generally start at step S1400 where a current picture form acoded video bitstream is acquired. The process proceeds to step S1402,where a first motion vector predictor of a first neighboring block of acurrent block in the current picture is selected from a HMVP buffer. Forexample, the first motion vector predictor is selected from the HMVPbuffer illustrated in FIGS. 10A and 10B. The process proceeds to stepS1404, where a second motion vector predictor of a first neighboringblock of the current block in the current picture is selected from theHMVP buffer. For example, the second motion vector predictor is selectedfrom the HMVP buffer illustrated in FIGS. 10A and 10B.

The process proceeds to step S1406, where a first temporal blockincluded in a previously decoded reference picture associated with thecurrent picture is selected, where the first temporal block includes athird motion vector predictor. For example, the temporal block in thereference picture is selected from one of candidate locations C0-C8, asillustrated in FIG. 13. The process proceeds to step S1408, where afinal motion vector predictor is determined from the first, second, andthird motion vector predictors.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 15 shows a computersystem (1500) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 15 for computer system (1500) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1500).

Computer system (1500) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1501), mouse (1502), trackpad (1503), touchscreen (1510), data-glove (not shown), joystick (1505), microphone(1506), scanner (1507), camera (1508).

Computer system (1500) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1510), data-glove (not shown), or joystick (1505), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1509), headphones(not depicted)), visual output devices (such as screens (1510) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1500) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1520) with CD/DVD or the like media (1521), thumb-drive (1522),removable hard drive or solid state drive (1523), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1500) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1549) (such as, for example USB ports of thecomputer system (1500)); others are commonly integrated into the core ofthe computer system (1500) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1500) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1540) of thecomputer system (1500).

The core (1540) can include one or more Central Processing Units (CPU)(1541), Graphics Processing Units (GPU) (1542), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1543), hardware accelerators for certain tasks (1544), and so forth.These devices, along with Read-only memory (ROM) (1545), Random-accessmemory (1546), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1547), may be connectedthrough a system bus (1548). In some computer systems, the system bus(1548) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1548),or through a peripheral bus (1549). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1541), GPUs (1542), FPGAs (1543), and accelerators (1544) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1545) or RAM (1546). Transitional data can be also be stored in RAM(1546), whereas permanent data can be stored for example, in theinternal mass storage (1547). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1541), GPU (1542), massstorage (1547), ROM (1545), RAM (1546), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1500), and specifically the core (1540) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1540) that are of non-transitorynature, such as core-internal mass storage (1547) or ROM (1545). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1540). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1540) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RANI (1546) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1544)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   33 Oblon Docket No.: 517836US-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

(1) A method of video decoding for a video decoder includes acquiring acurrent picture from a coded video bitstream; selecting, from a historybuffer that stores motion vector predictors of N previously decodedblocks from the current picture, a first motion vector predictor of afirst neighboring block of a current block in the current picture, Nbeing an integer greater than 1; selecting, from the history buffer, asecond motion vector predictor of a second neighboring block of thecurrent block; selecting a first temporal block included in a previouslydecoded reference picture associated with the current picture, the firsttemporal block including a third motion vector predictor, the firsttemporal block being one of (i) neighboring to a collocated block of thecurrent block and (ii) within the collocated block; and determining amotion vector predictor of the current block using a weighted average ofthe first motion vector predictor, the second motion vector predictor,and the third motion vector predictor.

(2) The method according to feature (1), in which the history buffer isa first-in-first-out (FIFO) buffer, and each entry in the history bufferincludes (i) x and y coordinates of a previously decoded block in thecurrent picture and (ii) the motion vector predictor of the previouslydecoded block.

(3) The method according to feature (2), in which the step of selectingthe first motion vector predictor further includes selecting, as thefirst motion vector predictor, a motion vector predictor of the lastentry in the history buffer that has a previously decoded block with a xcoordinate that is less than a x coordinate of the current block.

(4) The method according to feature (3), in which the step of selectingthe second motion vector predictor further includes selecting, as thesecond motion vector predictor, the last entry in the history bufferthat has a previously decoded block with a y coordinate that is smallerthan a y coordinate of the current block.

(5) The method according to any one of features (2)-(4), the methodfurther includes for each entry in the history buffer that has apreviously decoded block with a x coordinate that is less than a xcoordinate of the current block, determining a difference between the xcoordinate of the previously decoded block and the x coordinate of thecurrent block, in which the step of selecting the first motion vectorpredictor further includes, selecting, as the first motion vectorpredictor, a motion vector predictor of the entry in the history bufferwith a previously decoded block having the largest determined differencein x coordinates with the current block.

(6) The method according to feature (5), further including for eachentry in the history buffer that has a previously decoded block with a ycoordinate that is greater than a y coordinate of the current block,determining a difference between the y coordinate of the previouslydecoded block and the y coordinate of the current block, in which thestep of selecting the second motion vector predictor further includes,selecting, as the second motion vector predictor, a motion vectorpredictor of the entry in the history buffer with a previously decodedblock having the largest determined difference in y coordinates with thecurrent block.

(7) The method according to any one of features (1)-(6), furtherincluding determining a frequency of occurrence of each motion vectorpredictor of each entry in the history buffer, in which the motionvector predictor with the largest frequency of occurrence in the historybuffer is selected as the first motion vector predictor, and in whichthe motion vector predictor with the second largest frequency ofoccurrence in the history buffer is selected as the second motion vectorpredictor.

(8) The method according to any one features (1)-(7), further includingselecting, from the history buffer, a third motion vector predictor of athird neighboring block of the current block from the history buffer, inwhich the first, second, and third motion vector predictors are selectedfrom entries in the in the history buffer with the three most recentlydecoded blocks in the current picture, and in which the determining amotion vector predictor of the current block further includes using aweighted average of the first, second, and third motion vectorpredictors.

(9) The method according to any one of features (1)-(8), furtherincluding selecting a second temporal block included in the previouslydecoded reference picture associated with the current picture, thesecond temporal block including a fourth motion vector predictor, thesecond temporal block being one of (i) neighboring to the collocatedblock of the current block and (ii) within the collocated block, and inwhich the determining the motion vector predictor of the current blockfurther includes using a weighted average of the first, second, third,and fourth motion vector predictors.

(10) The method according to feature (8) or (9), in which the firsttemporal block in the reference picture is neighboring to the collocatedblock of the current block and is selected from a group consisting of(i) a block that neighbors a bottom left corner of the collocated block,(ii) a block that is aligned with a block that is in the center of thecollocated block, and (iii) a block that neighbors a bottom right cornerof the collocated block.

(11) The method according to feature (9) or (10), in which the secondtemporal block in the reference picture is within the collocated blockof the current block and is selected from a group consisting of (i) ablock in the center of the collocated block, (ii) a block that is abovethe center of the collocated block, (iii) a block that is to the left ofthe center of the collocated block, and (iv) a block that is to theright of the center of the collocated block.

(12) A video decoder for video decoding includes processing circuitryconfigured to acquire a current picture from a coded video bitstream,select, from a history buffer that stores motion vector predictors of Npreviously decoded blocks from the current picture, a first motionvector predictor of a first neighboring block of a current block in thecurrent picture, N being an integer greater than 1, select, from thehistory buffer, a second motion vector predictor of a second neighboringblock of the current block, select a first temporal block included in apreviously decoded reference picture associated with the currentpicture, the first temporal block including a third motion vectorpredictor, the first temporal block being one of (i) neighboring to acollocated block of the current block and (ii) within the collocatedblock, and determine a motion vector predictor of the current blockusing a weighted average of the first motion vector predictor, thesecond motion vector predictor, and the third motion vector predictor.

(13) The video decoder according to feature (12), in which the historybuffer is a first-in-first out (FIFO) buffer, and each entry in thehistory buffer includes (i) x and y-coordinates of a previously decodedblock in the current picture and (ii) the motion vector predictor of thepreviously decoded block.

(14) The video decoder according to feature (13), in which the selectionof the first motion vector predictor further includes the processingcircuitry configured to select, as the first motion vector predictor, amotion vector predictor of the last entry in the history buffer that hasa previously decoded block with a x coordinate that is less than a xcoordinate of the current block.

(15) The video decoder according to feature (14), in which the selectionof the second motion vector predictor further includes the processingcircuitry configured to select, as the second motion vector predictor,the last entry in the history buffer that has a previously decoded blockwith a y coordinate that is smaller than a y coordinate of the currentblock.

(16) The video decoder according to any one of features (13)-(15), inwhich the processing circuitry is further configured to for each entryin the history buffer that has a previously decoded block with a xcoordinate that is less than a x coordinate of the current block,determine a difference between the x coordinate of the previouslydecoded block and the x coordinate of the current block, in which theselection of the first motion vector predictor further includes, theprocessing circuitry configured to select, as the first motion vectorpredictor, a motion vector predictor of the entry in the history bufferwith a previously decoded block having the largest determined differencein x coordinates with the current block.

(17) The video decoder according to feature (16), in which theprocessing circuitry is further configured to: for each entry in thehistory buffer that has a previously decoded block with a y coordinatethat is greater than a y coordinate of the current block, determine adifference between the y coordinate of the previously decoded block andthe y coordinate of the current block, in which the selection of thesecond motion vector predictor further includes the processing circuitryconfigured to select, as the second motion vector predictor, a motionvector predictor of the entry in the history buffer with a previouslydecoded block having the largest determined difference in y coordinateswith the current block.

(18) The video decoder according to any one of features (12)-(17), inwhich the processing circuitry is further configured to determine afrequency of occurrence of each motion vector predictor of each entry inthe history buffer, in which the motion vector predictor with thelargest frequency of occurrence in the history buffer is selected as thefirst motion vector predictor, and in which the motion vector predictorwith the second largest frequency of occurrence in the history buffer isselected as the second motion vector predictor.

(19) The video decoder according to any one of features (12)-(18), inwhich the processing circuitry is further configured to: select, fromthe history buffer, a third motion vector predictor of a thirdneighboring block of the current block from the history buffer, in whichthe first, second, and third motion vector predictors are selected fromentries in the in the history buffer with the three most recentlydecoded blocks in the current picture, and in which the determination ofthe motion vector predictor of the current block further includes usinga weighted average of the first, second, and third motion vectorpredictors.

(20) A non-transitory computer readable medium having instructionsstored therein, which when executed by a processor in a video decodercauses the video decoder to execute a method including acquiring acurrent picture from a coded video bitstream; selecting, from a historybuffer that stores motion vector predictors of N previously decodedblocks from the current picture, a first motion vector predictor of afirst neighboring block of a current block in the current picture, Nbeing an integer greater than 1; selecting, from the history buffer, asecond motion vector predictor of a second neighboring block of thecurrent block; selecting a first temporal block included in a previouslydecoded reference picture associated with the current picture, the firsttemporal block including a third motion vector predictor, the firsttemporal block being one of (i) neighboring to a collocated block of thecurrent block and (ii) within the collocated block; and determining amotion vector predictor of the current block using a weighted average ofthe first motion vector predictor, the second motion vector predictor,and the third motion vector predictor.

1. A method of video decoding for a video decoder, comprising: acquiringa current picture from a coded video bitstream; selecting a first motionvector predictor of a first neighboring block of a current block, thefirst motion vector predictor is selected from a first-in-first-out(FIFO) history buffer that stores motion vector predictors and (ii) xand y coordinates of N previously decoded blocks from the currentpicture. each motion vector predictor being stored in association with xand y coordinates of a corresponding one of the previously decodedblocks, wherein the selected first motion vector predictor is a lastentry in the history buffer among entries with a x coordinate that isless than a x coordinate of the current block, N being an integergreater than 1; selecting, from the history buffer, a second motionvector predictor of a second neighboring block of the current block;selecting a first temporal block included in a previously decodedreference picture associated with the current picture, the firsttemporal block including a third motion vector predictor, the firsttemporal block being one of (i) neighboring to a collocated block of thecurrent block and (ii) within the collocated block; and determining amotion vector predictor of the current block using a weighted average ofthe first motion vector predictor, the second motion vector predictor,and the third motion vector predictor.
 2. (canceled)
 3. (canceled) 4.The method according to claim I, wherein the selecting the second motionvector predictor further includes selecting, as the second motion vectorpredictor, a last entry in the history buffer among entries with a ycoordinate that is smaller than a y coordinate of the current block. 5.The method according to claim 1, further comprising: for each entry inthe history buffer associated with a x coordinate that is less than thex coordinate of the current block, determining a difference between thex coordinate of the respective entry and the x coordinate of the currentblock, wherein the selecting the second motion vector predictor furtherincludes, selecting, as the second motion vector predictor, a motionvector predictor of the entry in the history buffer having a largestdetermined difference in x coordinates with the current block.
 6. Themethod according to claim 1, further comprising: for each entry in thehistory buffer associated with a y coordinate that is greater than a ycoordinate of the current block, determining a difference between the ycoordinate of the respective entry and the y coordinate of the currentblock, wherein the step of selecting the second motion vector predictorfurther includes, selecting, as the second motion vector predictor, amotion vector predictor of the entry in the history buffer having alargest determined difference in v coordinates with the current block.7. The method according to claim I, further comprising: determining afrequency of occurrence of each motion vector predictor of each entry inthe history buffer, wherein the motion vector predictor with a largestfrequency of occurrence in the history buffer is selected as the secondmotion vector predictor, wherein the motion vector predictor with asecond largest frequency of occurrence in the history buffer is selectedas a fourth motion vector predictor, and wherein the motion vectorpredictor of the current block is a weighted average of the first motionvector predictor, the second motion vector predictor, the third motionvector predictor, and the fourth motion vector predictor.
 8. The methodaccording to claim I, further comprising: selecting, from the historybuffer, a fourth motion vector predictor of a third neighboring block ofthe current block, wherein the second and fourth motion vecta p dictorsare selected from entries in the history buffer corresponding to twomost recently decoded blocks in the current picture, and wherein thedetermining the motion vector predictor of the current block furtherincludes using a weighted average of the first, second, third, andfourth motion vector predictors.
 9. The method according to claim I,further comprising: selecting a second temporal block included in thepreviously decoded reference picture associated with the currentpicture, the second temporal block including a fourth motion vectorpredictor, the second temporal block being one of (i) neighboring to thecollocated block of the current block and (ii) within the collocatedblock, and wherein the determining the motion vector predictor of thecurrent block further includes using a weighted average of the first,second, third, and fourth motion vector predictors.
 10. The methodaccording to claim 8, wherein the first temporal block in the referencepicture is neighboring to the collocated block of the current block andis selected from a group consisting of (i) a block that neighbors abottomleft corner of the collocated block, (ii) a block that is alignedwith a block that is in a center of the collocated block, and (iii) ablock that neighbors a bottom right corner of the collocated block. 11.The method according to claim 9, wherein the second temporal block inthe previously decoded reference picture is within the collocated blockof the current block and is selected from a group consisting of (i) ablock in a center of the collocated block, (ii) a block that is abovethe center of the collocated block, (iii) a block that is left of thecenter of the collocated block, and (iv) a block that is right of thecenter of the collocated block.
 12. A video decoder for video decoding,comprising: processing circuitry configured to: acquire a currentpicture from a coded video bitstream, select a first motion vectorpredictor of a first neighboring block of a. current block the firstmotion vector predictor is selected from a first-in-first-out (FIFO)history buffer that stores motion vector predictors of N previouslydecoded blocks from the current picture, each motion vector predictorbeing stored in association with x and v coordinates of a correspondingone of the previously decoded blocks, wherein the selected first motionvector predictor is a last entry in the history buffer among entrieswith a x coordinate that is less than a x coordinate of the currentblock, N being an integer greater than 1, select, from the historybuffer, a second motion vector predictor of a second neighboring blockof the current block, select a first temporal block included in apreviously decoded reference picture associated with the currentpicture, the first temporal block including a third motion vectorpredictor, the first temporal block being one of (i) neighboring to acollocated block of the current block and (ii) within the collocatedblock; and determine a motion vector predictor of the current blockusing a weighted average of the first motion vector predictor, thesecond motion vector predictor, and the third motion vector predictor.13. (canceled)
 14. (canceled)
 15. The video decoder according to claim12, wherein the selection of the second motion vector predictor furtherincludes the processing circuitry configured to select, as the secondmotion vector predictor, a last entry in the history buffer amongentries with a y coordinate that is smaller than a y coordinate of thecurrent block.
 16. The video decoder according to claim 12, wherein theprocessing circuitry is further configured to: for each entry in thehistory buffer associated with a x coordinate that is less than the xcoordinate of the current block, determine a difference between the xcoordinate of the respective entry and the x coordinate of the currentblock, wherein the selection of the second motion vector predictorfurther includes, the processing circuitry configured to select, as thesecond motion vector predictor, a motion vector predictor of the entryin the history buffer having a largest determined difference in xcoordinates with the current block.
 17. The video decoder according toclaim 12, wherein the processing circuitry is further configured to: foreach entry in the history buffer associated with a y coordinate that isgreater than a y coordinate of the current block, determine a differencebetween the y coordinate of the respective entry and the y coordinate ofthe current block, wherein the selection of the second motion vectorpredictor further includes the processing circuitry configured toselect, as the second motion vector predictor, a motion vector predictorof the entry in the history buffer having a largest determineddifference in y coordinates with the current block.
 18. The videodecoder according to claim 12, wherein the processing circuitry isfurther configured to: determine a frequency of occurrence of eachmotion vector predictor of each entry in the history buffer, wherein themotion vector predictor with a largest frequency of occurrence in thehistory buffer is selected as the second motion vector predictor,wherein the motion vector predictor with a second largest frequency ofoccurrence in the history buffer is selected as a fourth motion vectorpredictor, and wherein the motion vector predictor of the current blockis a weighted average of the first motion vector predictor, the secondmotion vector predictor, the third motion vector predictor, and thefourth motion vector predictor.
 19. The video decoder according to claim12, wherein the processing circuitry is further configured to: select,from the history buffer, a fourth motion vector predictor of a thirdneighboring block of the current block, wherein the second and fourthmotion vector predictors are selected from entries in the history buffercorresponding to two most recently decoded blocks in the currentpicture, and wherein the determination of the motion vector predictor ofthe current block further includes using a weighted average of thefirst, second, third, and fourth motion vector predictors.
 20. Anon-transitory computer readable medium having instructions storedtherein, which when executed by a processor in a video decoder causesthe video decoder to execute a method comprising: acquiring a currentpicture from a coded video bitstream; selecting a first motion vectorpredictor of a first neighboring block of a current block, the firstmotion vector is selected from a first-in-first-out (FIFO) historybuffer that stores motion vector predictors of N previously decodedblocks from the current picture, each motion vector predictor beingstored in association with x and y coordinates of a corresponding one ofthe previously decoded blocks, wherein the selected first motion vectorpredictor is a last entry in the history buffer among entries with a xcoordinate that is less than a x coordinate of the current block, Nbeing an integer greater than 1; selecting, from the history buffer, asecond motion vector predictor of a second neighboring block of thecurrent block; selecting a first temporal block included in a previouslydecoded reference picture associated with the current picture, the firsttemporal block including a third motion vector predictor, the firsttemporal block being one of (i) neighboring to a collocated block of thecurrent block and (ii) within the collocated block; and determining amotion vector predictor of the current block using a weighted average ofthe first motion vector predictor, the second motion vector predictor,and the third motion vector predictor.